Methods and systems for fast filter change

ABSTRACT

A system is provided for fasting switching a filter of an imaging system during a scan. In one embodiment, a system comprises a computation device with instructions stored in a non-transient memory to emit an X-ray beam via an X-ray source; move an imaging subject via a motorized table at a nonzero speed; while moving the imaging subject, acquire a dataset of the imaging subject by detecting attenuated X-rays transmitted through the imaging subject via an X-ray detector, wherein a first filter is positioned within the X-ray beam, between the X-ray source and the imaging subject; and while acquiring the dataset, responsive to a change in an anatomy of the imaging subject to be imaged, operate a filter driving system to switch from the first filter to a second filter, wherein during filter switching, the X-ray source does not emit X-rays.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of and claimspriority to U.S. patent application Ser. No. 15/813,068, filed on Nov.14, 2017, the entirety of which is incorporated herein by reference.

BACKGROUND

Embodiments of the subject matter disclosed herein relate to diagnosticmedical imaging, and more particularly, to contrast enhanced computedtomography imaging.

Noninvasive imaging modalities may transmit energy in the form of X-rayradiation into an imaging subject. Based on the transmitted energy,images may be subsequently generated indicative of the structural orfunctional information internal to the imaging subject. In computedtomography (CT) imaging systems, X-rays are transmitted from an X-raysource to an X-ray detector through the imaging subject. A bowtie filtermay be positioned between the X-ray source and the imaging subject foradjusting the spatial distribution of the radiation energy based on theanatomy of the imaging subject. For example, a human body in the axialplane is thicker in the middle and thinner on the periphery. The bowtiefilter may be designed to distribute higher radiation energy to themiddle and less radiation energy to the peripheral of the subject. As aresult, the amplitude of signal received by the imaging detector isequalized, and the X-ray radiation dose on the periphery of the imagingsubject is reduced. Different anatomy of the subject may requiredifferent bowtie filters. For example, bowtie filters of different shapeand size may be designed to image the head, the chest, and the abdomenof the human body.

To further enhance contrast of specific organ and/or tissue type, anexternal contrast agent may be injected into the imaging subject. Theduration for acquiring the contrast enhanced images may be short due tolimited contrast agent circulation time at the anatomy being imaged.Therefore, a method for acquiring high quality contrast enhanced imagesacross different anatomies of the subject, wherein different bowtiefilters are required for imaging each of the anatomies, is needed.

BRIEF DESCRIPTION

In an aspect, an imaging system, comprising a gantry for receiving animaging subject; an X-ray source positioned in the gantry for emittingan X-ray beam; an X-ray detector positioned in the gantry opposite tothe X-ray source; a filter assembly mounted in the gantry; a firstfilter and a second filter positioned in the filter assembly; a filterdriving system for switching filters by moving filters into or out ofthe X-ray beam; a motorized table for moving an imaging subject; and acomputation device with instructions stored in a non-transient memory toemit the X-ray beam via the X-ray source; move the imaging subject viathe motorized table at a nonzero speed; while moving the imagingsubject, acquire a dataset of the imaging subject by detectingattenuated X-rays transmitted through the imaging subject via the X-raydetector, wherein a first filter is positioned within the X-ray beam,between the X-ray source and the imaging subject; and while acquiringthe dataset, responsive to a change in an anatomy of the imaging subjectto be imaged, operate the filter driving system to switch from the firstfilter to a second filter, wherein during filter switching, the X-raysource does not emit X-rays.

It should be understood that the brief description above is provided tointroduce in simplified form a selection of concepts that are furtherdescribed in the detailed description. It is not meant to identify keyor essential features of the claimed subject matter, the scope of whichis defined uniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present application will be better understood from reading thefollowing description of non-limiting embodiments, with reference to theattached drawings, wherein below:

FIG. 1 shows a pictorial view of an imaging system according to anembodiment of the invention.

FIG. 2 shows a block schematic diagram of an exemplary imaging systemaccording to an embodiment of the invention.

FIG. 3 shows flow chart of an example method for contrast enhancedimaging using multiple filters.

FIG. 4A shows an example timeline of contrast enhanced imaging accordingto the example method of FIG. 3.

FIG. 4B illustrates sections of an imaging subject that is imaged duringthe example timeline of FIG. 4A.

FIG. 5 shows another example timeline of contrast enhanced imagingaccording to the example method of FIG. 3.

FIG. 6 shows flow chart of an example method for imaging multiplesections of an imaging subject with different anatomies.

FIG. 7 shows an example timeline while implementing the method of FIG.6.

FIG. 8A shows a first position of a filter assembly with three filters.

FIG. 8B shows a second position of the filter assembly of FIG. 8A.

FIG. 8C shows a third position of the filter assembly of FIG. 8A.

FIG. 8D shows a fourth position of the filter assembly of FIG. 8A.

FIG. 9A shows one example configuration of a filter driving system.

FIG. 9B shows another example configuration of a filter driving system.

DETAILED DESCRIPTION

The following description relates to various embodiments of contrastenhanced imaging. In particular, systems and methods are provided forcontrast enhanced CT imaging using more than one bowtie filter. FIGS.1-2 show an example embodiment of an imaging system, wherein a filter ispositioned between the X-ray source and the imaging subject. Differentfilters may be selected based on the anatomy of the imaging subjectbeing imaged. FIG. 3 shows an example method of contrast enhanced CTimaging with fast switching bowtie filters. In particular, aftercontrast agent injection, the bowtie filter is switched before imaging adifferent section of the subject by operating a filter driving system.FIG. 4A shows an example timeline of CT imaging and filter switchingwith respect to the contrast agent enhancement in the imaging subject.FIG. 4B illustrates sections of the subject that have been imaged duringthe timeline of FIG. 4A. FIG. 5 shows another example timeline of CTimaging and filter switching, wherein images are acquired at multipletime points to track variation of the contrast enhancement in thesubject over time. The fast filter switching may also be used for fastimaging of multiple sections of the imaging subject, as shown in FIGS.6-7. FIGS. 8A-8D show various positions of an example filter assemblywith three filters. FIGS. 9A-9B show detailed configuration of thefilter driving system.

Though a CT imaging system is described by way of example, it should beunderstood that the present techniques may also be useful when appliedto images acquired using other imaging modalities, such astomosynthesis, C-arm angiography, and so forth. The present discussionof a CT imaging modality is provided merely as an example of onesuitable imaging modality.

Various embodiments may be implemented in connection with differenttypes of imaging systems. For example, various embodiments may beimplemented in connection with a CT imaging system in which an X-raysource projects a fan or cone shaped X-ray beam that is collimated tolie within an x-y plane of a Cartesian coordinate system and generallyreferred to as an “imaging plane.” The X-ray beam passes through animaging subject, such as a patient. The X-ray beam, after beingattenuated by the imaging subject, impinges upon an X-ray detectorarray. The intensity of the attenuated X-ray beam received at thedetector array is dependent upon the attenuation of an X-ray beam by theimaging subject. Each detector element of the array produces a separateelectrical signal that is a measurement of the beam intensity at thedetector location. The intensity measurement from all the detectors isacquired separately to produce a transmission profile.

In CT imaging systems, the X-ray source and the detector array arerotated with a gantry within the imaging plane and around the object tobe imaged such that the angle at which the X-ray beam intersects theimaging subject constantly changes. A complete gantry rotation occurswhen the gantry concludes one full 360 degree rotation. A group of X-rayattenuation measurements (e.g., projection data) from the detector arrayat one gantry angle is referred to as a “view.” A view is, therefore,each incremental position of the gantry. A “scan” of the objectcomprises a set of views made at different gantry angles, or viewangles, during one revolution of the X-ray source and detector.

In an axial scan, the projection data is processed to construct an imagethat corresponds to a two-dimensional slice taken through the imagingsubject. One method for reconstructing an image from a set of projectiondata is referred to in the art as a filtered backprojection technique.This process converts the attenuation measurements from a scan intointegers called “CT numbers” or “Hounsfield units” (HU), which are usedto control the brightness of a corresponding pixel on a display.

FIG. 1 illustrates an exemplary CT imaging system 100 configured toallow fast and iterative image reconstruction. Particularly, the CTimaging system 100 is configured to image a subject such as a patient,an inanimate object, one or more manufactured parts, and/or foreignobjects such as dental implants, stents, and/or contrast agents presentwithin the body. In one embodiment, the CT imaging system 100 includes agantry 102, which in turn, may further include an X-ray source 104configured to project a beam of X-rays 106 for use in imaging a subject.Specifically, the X-ray source 104 is configured to project the X-raybeam 106 towards an X-ray detector array 108 positioned on the oppositeside of the gantry 102. Although FIG. 1 depicts only a single X-raysource 104, in certain embodiments, multiple X-ray sources may beemployed to project a plurality of X-ray beams 106 for acquiringprojection data corresponding to the patient at different energy levels.

In certain embodiments, the CT imaging system 100 further includes animage processing unit 110 configured to reconstruct images of a targetvolume of the patient using an iterative or analytic imagereconstruction method. For example, the image processing unit 110 mayuse an analytic image reconstruction approach such as filteredbackprojection (FBP) to reconstruct images of a target volume of thepatient. As another example, the image processing unit 110 may use aniterative image reconstruction approach such as advanced statisticaliterative reconstruction (ASIR), conjugate gradient (CG), maximumlikelihood expectation maximization (MLEM), model-based iterativereconstruction (MBIR), and so on to reconstruct images of a targetvolume of the patient.

FIG. 2 illustrates an exemplary imaging system 200 similar to the CTimaging system 100 of FIG. 1. In accordance with aspects of the presentdisclosure, the system 200 is configured to perform automatic exposurecontrol responsive to user input. In one embodiment, the system 200includes the detector array 108 (see FIG. 1). The detector array 108further includes a plurality of detector elements 202 that togethersense the X-ray beam 106 (see FIG. 1) that pass through a subject 204such as a patient to acquire corresponding projection data. Accordingly,in one embodiment, the detector array 108 is fabricated in a multi-sliceconfiguration including the plurality of rows of cells or detectorelements 202. In such a configuration, one or more additional rows ofthe detector elements 202 are arranged in a parallel configuration foracquiring the projection data.

A bowtie filter housing 240 may be mounted within gantry 102 betweenX-ray source 104 and the subject 204. The bowtie filter may change theenergy distribution of the X-ray beam in the axial plane of the imagingsubject (such as a patient). For example, the re-distributed X-ray beammay have higher energy at the center and lower energy at the peripheryof the subject. One or more bowtie filters may be positioned within thefilter housing 240. Each and every bowtie filter is rigid andnon-deformable. Each of the bowtie filters may be designed to image aspecific anatomy or section of the human body, such as head, chest, andabdomen. Three different bowtie filters 241, 242, and 243 are shown inFIG. 2 as an example. The bowtie filters are shown here in rectangularshape as an example. The bowtie filters alternatively be in differentshapes and materials to provide proper X-ray special spectrum forimaging various types of anatomies. During imaging, one of the bowtiefilters may be selected based on the anatomy of the subject, and beplaced into the X-ray beam path. Responsive to a change in the anatomy,the filter may be changed from one to another. Example arrangement ofthe filters in the filter housing is shown in FIGS. 8A-8D. A filterdriving system (not shown here) may be coupled to the filter to move thefilter into and out of the X-ray beam path. Examples of the filterdriving system are shown in FIGS. 9A-9B. In one embodiment, the motormay couple the filters through a shaft. The bowtie filters may beswitched from one to another by translating the filters along the shaftby rotating the shaft with a motor. One of the filters may be selectedand translated into the X-ray beam between the X-ray source and theimaging subject to image a specific section of the human body. Computingdevice 216 may send command to the motor of the filter driving system tomove the selected filter in to the X-ray beam. The filter driving systemmay also send filter position information back to the computing device216.

In certain embodiments, the system 200 is configured to traversedifferent angular positions around the subject 204 for acquiring desiredprojection data. Accordingly, the gantry 102 and the components mountedthereon (such as the X-ray source 104, the filter housing 240, and thedetector 202) may be configured to rotate about a center of rotation 206for acquiring the projection data, for example, at different energylevels. Alternatively, in embodiments where a projection angle relativeto the subject 204 varies as a function of time, the mounted componentsmay be configured to move along a general curve rather than along asegment of a circle.

In one embodiment, the system 200 includes a control mechanism 208 tocontrol movement of the components such as rotation of the gantry 102and the operation of the X-ray source 104. In certain embodiments, thecontrol mechanism 208 further includes an X-ray controller 210configured to provide power and timing signals to the X-ray source 104.Additionally, the control mechanism 208 includes a gantry motorcontroller 212 configured to control a rotational speed and/or positionof the gantry 102 based on imaging requirements.

In certain embodiments, the control mechanism 208 further includes adata acquisition system (DAS) 214 configured to sample analog datareceived from the detector elements 202 and convert the analog data todigital signals for subsequent processing. The data sampled anddigitized by the DAS 214 is transmitted to a computing device (alsoreferred to as processor) 216. In one example, the computing device 216stores the data in a storage device 218. The storage device 218, forexample, may include a hard disk drive, a floppy disk drive, a compactdisk-read/write (CD-R/W) drive, a Digital Versatile Disc (DVD) drive, aflash drive, and/or a solid-state storage device.

Additionally, the computing device 216 provides commands and parametersto one or more of the DAS 214, the X-ray controller 210, and the gantrymotor controller 212 for controlling system operations such as dataacquisition and/or processing. In certain embodiments, the computingdevice 216 controls system operations based on operator input. Thecomputing device 216 receives the operator input, for example, includingcommands and/or scanning parameters via an operator console 220operatively coupled to the computing device 216. The operator console220 may include a keyboard (not shown) or a touchscreen to allow theoperator to specify the commands and/or scanning parameters.

Although FIG. 2 illustrates only one operator console 220, more than oneoperator console may be coupled to the system 200, for example, forinputting or outputting system parameters, requesting examinations,and/or viewing images. Further, in certain embodiments, the system 200may be coupled to multiple displays, printers, workstations, and/orsimilar devices located either locally or remotely, for example, withinan institution or hospital, or in an entirely different location via oneor more configurable wired and/or wireless networks such as the Internetand/or virtual private networks.

In one embodiment, for example, the system 200 either includes, or iscoupled to a picture archiving and communications system (PACS) 224. Inan exemplary implementation, the PACS 224 is further coupled to a remotesystem such as a radiology department information system, hospitalinformation system, and/or to an internal or external network (notshown) to allow operators at different locations to supply commands andparameters and/or gain access to the image data.

The computing device 216 uses the operator-supplied and/orsystem-defined commands and parameters to operate a table motorcontroller 226, which in turn, may control a motorized table 228.Particularly, the table motor controller 226 moves the table 228 forappropriately positioning the subject 204 in the gantry 102 foracquiring projection data corresponding to the target volume of thesubject 204.

As previously noted, the DAS 214 samples and digitizes the projectiondata acquired by the detector elements 202. Subsequently, an imagereconstructor 230 uses the sampled and digitized X-ray data to performhigh-speed reconstruction. Although FIG. 2 illustrates the imagereconstructor 230 as a separate entity, in certain embodiments, theimage reconstructor 230 may form part of the computing device 216.Alternatively, the image reconstructor 230 may be absent from the system200 and instead the computing device 216 may perform one or morefunctions of the image reconstructor 230. Moreover, the imagereconstructor 230 may be located locally or remotely, and may beoperatively connected to the system 100 using a wired or wirelessnetwork. Particularly, one exemplary embodiment may use computingresources in a “cloud” network cluster for the image reconstructor 230.

In one embodiment, the image reconstructor 230 stores the imagesreconstructed in the storage device 218. Alternatively, the imagereconstructor 230 transmits the reconstructed images to the computingdevice 216 for generating useful patient information for diagnosis andevaluation. In certain embodiments, the computing device 216 transmitsthe reconstructed images and/or the patient information to a display 232communicatively coupled to the computing device 216 and/or the imagereconstructor 230.

Turning to FIG. 3, an example method 300 for performing contrastenhanced imaging with multiple filters is presented. To achieve highimage quality, it is optimal to perform the contrast enhanced imaging athigh X-ray attenuation of the targeting anatomy. In other words, it isoptimal to perform the contrast enhanced imaging at high contrast agentenhancement. The amount of the attenuation, or the degree of contrastenhancement, may be measured by the CT numbers. For example, increasedattenuation or increased contrast enhancement corresponds to high CTnumbers. Further, it is preferable to minimize the dose of the contrastagent and the number of contrast injections during scan. Method 300achieves fast image acquisition of multiple anatomies of the imagingsubject by fast changing the filters during the scan.

Method 300 may be performed according to instructions stored in thenon-transitory memory in a computing device (such as computer 216 ofFIG. 2) of the imaging system. In particular, after the contrast agentis injected into the imaging subject, a first section of the subject isimaged using a first filter. After fast filter switching, a second,different, section of the subject is imaged with a second filter. Thefirst and the second sections may have different anatomies. As such,contrast enhanced images of different anatomies of the subject may beacquired with a one-time contrast agent injection. Herein, a section ofthe subject is a three-dimensional volume along the length of a humanbody.

At 302, method 300 includes setting up scan parameters. For example, auser may input or select the scan parameters according to a scanningprotocol or a menu. The scan parameters may include the type andsequence of the filters that are going to be used during the scan. Thetype of the filters may be chosen based on the anatomy of imagingsubject that is to be imaged. Method 300 may also include setting scantiming. As one example, the scan timing may include a start time and aduration for imaging each section. As another example, method 300 mayinclude setting up one or more contrast enhancement thresholds, and theimaging of each section may start responsive to the actual contrastagent enhancement reaching the thresholds. Method 300 may also includeloading anatomy information of the imaging subject to the memory of thecomputation device. The anatomy information may be acquired from apre-scan. This step may also include moving the first filter to aposition in the X-ray beam path between the X-ray source and thesubject, and moving the subject so that the first section of the subjectis within the gantry for imaging. The type of the first filter isdetermined based on the anatomy of the first section of the subject.

At 304, contrast agent is injected into the imaging subject. Method 300starts monitoring the enhancement of the contrast agent within thesubject, at the anatomy of interest. As one example, the contrast agentenhancement at the anatomy of interest may be monitored by periodicallyimaging the same location of the subject and analyzing the change ifcontrast enhancement over time. As another example, the enhancement ofthe contrast agent in one section of the subject may be derived from thecontrast enhancement in another section of the subject. As yet anotherexample, the contrast enhancement may be estimated based on time elapsedsince injection based on empirical knowledge of the physiologicalcirculation time of the contrast agent in the anatomy of interest. Asone example, the physiological circulation time of the contrast agentmay be the circulation time of blood. The estimated enhancement mayfurther be adjusted based on the dose of the contrast and the mass ofthe subject. For example, the estimated enhancement may increase withthe increased contrast dose and decrease with the mass of the subject.

At 306, method 300 compares the estimated contrast agent enhancementwith a predetermined positive non-zero first threshold. The firstthreshold may be determined based on a predicted minimum concentrationof the contrast agent in the subject, as well as the duration andsequence of image acquisition as defined by the scan parametersdescribed above. The first threshold may be a sensitivity of the imagingsystem to the contrast agent in the imaged anatomy. In one example, thefirst threshold may be determined so that each dataset of each sectionof the subject is acquired at an enhancement (CT number) higher than thethreshold. For example, the first threshold may be slightly lower than apredicted maximum enhancement, such as 10% lower than the predictedmaximum enhancement. In this way, a plurality of imaging datasets may beobtained when the contrast enhancement is within a threshold range ofthe maximum enhancement (e.g., as the enhancement approaches, reaches,and then recedes from the maximum enhancement threshold). In oneembodiment, the contrast agent enhancement in a first section of thesubject is compared with the first threshold.

Responsive to the estimated enhancement being higher than the firstthreshold, method 300 proceeds to 310 to acquire an image dataset.Otherwise, method 300 moves to 308 to continue monitoring contrast agentenhancement.

At 310, method 300 starts acquiring the first dataset of the firstsection of the subject using the first filter. For example, the X-raysource (such as 104 of FIGS. 1-2) may be activated, and start emittingX-ray radiation exposure (such as 106 of FIGS. 1-2) to the imagingsubject through the first filter. The dataset is acquired from thedetector (such as 108 of FIG. 2) upon receiving the attenuated X-raybeam from the imaging subject. Herein, a dataset corresponds to theprojection data acquired during imaging a section of the subject. In oneexample, the first section of the subject may be imaged once. In anotherexample, the first section of the subject may be imaged multiple timesto capture the change of enhancement of the contrast agent in thesubject.

At 312, after acquiring the first dataset, the first filter is moved outof the X-ray beam path and the second filter is moved into the X-raybeam path. The first and the second filters may be moved by operatingone or more motors, such as shown in FIGS. 8A-8B, which show examplefilter driving systems. By moving the filters with a motor, filters maybe automatically switched quickly within one scan. In one example,switching one filter with another filter may be completed within twoseconds. Step 312 may also include moving the subject via the motorizedtable (such as motorized table of 228 in FIGS. 1-2) to a proper locationto start acquiring a second dataset. The filter switching and subjectrelocation may be performed simultaneously. The type of the secondfilter may be determined based on the anatomy of a second section of thesubject. The first section and the second section of the subject mayhave different anatomies (such as different size and shape), so thatdifferent filter types are used for imaging each section. As an example,the first section may be the chest and the second section may be theabdomen. As another example, the first section may be one of the chest,the head, and the abdomen, and the second section may be one of thehead, the chest, and the abdomen.

At 314, method 300 estimates the enhancement of the contrast agent andcompares it with a predetermined second threshold. Similar to 304, thecontrast agent enhancement may be monitored by periodically imaging atthe same location of the subject and analyzing the contrast enhancementover time. The contrast agent enhancement may alternatively bedetermined based on time elapsed since injection, the physiologicalcirculation time of the anatomy of interest, the dose of the contrast,and the mass of the subject. The second threshold may be determined sothat the average contrast enhancement while acquiring the first datasetis substantially the same as the average contrast enhancement whileacquiring the second dataset. Herein, the average contrast enhancementsare substantially the same means the difference between the averagecontrast enhancements is within a threshold range. For example, thedifference between the average contrast enhancements is within 1% (orother suitable range, such as 5%) of either the average contrastenhancement of the first dataset or the second dataset. In anotherembodiment, the second threshold may be determined so that the averagecontrast enhancement while acquiring the first dataset is the same asthe average contrast enhancement while acquiring the second dataset. Assuch, the degree of contrast enhancement of the first and the seconddatasets are the same. In one example, the second threshold may behigher than the first threshold. In one embodiment, the contrast agentenhancement in the second section of the subject is compared with thesecond threshold.

If the contrast enhancement is lower than the second threshold, method300 proceeds to 316 to acquire the second dataset. Otherwise, method 300continues to monitor contrast agent enhancement. In one embodiment,steps 314 and 316 may be skipped, and the second dataset is acquiredimmediately after filter switching at 312. Further, in some examples,the second dataset may be acquired when the contrast agent enhancementis lower than the second threshold yet still higher than the firstthreshold. In this way, the second dataset may be acquired after thecontrast agent enhancement has reached the maximum enhancement and is atthe approximate same enhancement as when the first dataset wascollected.

At 318, the second dataset of the second section of the subject isacquired with the second filter. At least in some examples, due to thefast switching of the filters, no additional contrast agent is injectedto the imaging subject between the acquisition of the first dataset andthe acquisition of the second dataset. As one example, the secondsection of the subject may be imaged once. As another example, thesecond section of the subject may be imaged multiple times to capturethe change of enhancement of the contrast agent in the subject.

At 320, the acquired first and second datasets are displayed and stored.In one embodiment, the first dataset and the second dataset may bere-constructed to form an image. The image may include the first and thesecond sections displayed on the display. The image may betwo-dimensional or three-dimensional. As one example, the re-constructedfirst and second datasets may be displayed with the same dynamic range(that is, the same range of signal amplitudes in the datasets aredisplayed), as the average contrast enhancement is substantially thesame for the first and the second dataset. As such, images of the firstand the second sections of the subject are comparable to each other, anddiagnosis may be made by analyzing the images acquired with one contrastagent injection. In another embodiment, data of the first and the seconddatasets that have the same average contrast enhancement may beselected, and then processed to be displayed together in one image.Images of the first and second sections of the subject acquired atvarious contrast enhancement may be generated to provide functionalinformation of the imaged organs. The first and the second dataset, aswell as the processed images may be saved in the storage of the imagingsystem.

Turning to FIG. 4A, an example timeline of contrast enhancement 430,status of the motor for driving the filters 440, and the status of theX-ray source 450 while implementing method 300 are shown. In graph 430,the y-axis is the enhancement of contrast agent in the imaging subject.The contrast enhancement increases as indicated by the arrow of they-axis. Curve 401 shows the contrast enhancement over time. In oneexample, curve 401 may be predetermined based on empirical knowledge(such as physiological circulation time) of the contrast agent, thedose, and the mass of the subject. In another example, curve 401 may beestimated or measured during the contrast enhanced imaging. For example,the contrast enhancement may be periodically estimated or measured.Curve 401 may be then generated by interpolating the estimated/measuredcontrast enhancement. In graph 440, the motor status may be on or off.When the motor is on, filters are switched. For example, the motor maybe activated to rotate a shaft coupled to the filters. By rotating theshaft, the filter maybe translated into and out of the X-ray beam path.In graph 450, the X-ray source status may be on or off. When the X-raysource is on, dataset of the imaging subject is acquired. In FIG. 4A,the x-axes indicate time. The time increases as indicated by the arrowsof the x-axes.

Prior to T1, scan parameters are set up. The first filter is positionedinto the X-ray beam path. At T1, contrast agent is injected into thesubject. Responsive to the contrast agent administration, the contrastenhancement increases with time from zero.

At T2, the contrast enhancement reaches the first nonzero threshold 412.Responsive to the contrast enhancement higher than the first threshold412, the X-ray source is turned on, and acquisition of the first datasetof the first section of the subject is started. Acquisition of the firstdataset proceeds from T2 to T3. FIG. 4B shows an example first section421 of the subject 112. The first section covers the chest, and thefirst filter is designed to image the chest. To complete the scan of thefirst section, a sequence of axial scans may be performed in thedirection along the length of the subject, as shown with arrow 423.

At T3, the imaging of the first section of the imaging subject ends, andthe X-ray source is turned off. Right after the acquisition of dataduring the first scan at T3, the filters are switched by activation ofthe motor, and the first filter is moved out of the path of X-rays andthe second filter is moved into the path. At T4, the filter switching iscompleted. Due to the fast switch of the filter, the average contrastenhancement is high during imaging. The duration from T3 to T4 may beless than two seconds. In one example, the subject may be moved startingfrom T3 to a new location for imaging the second section of the subject.The contrast agent enhancement keeps increasing from T2 to T3 and peaksat T5. In another example, the peak T5 of the contrast enhancement maybe anywhere between T3 and T6.

At T6, responsive to the contrast enhancement being lower than thesecond threshold 410, the second dataset is acquired from T6 to T7 withthe second filter. As one example, the second threshold may bedetermined so that the average contrast enhancement from T2 to T3 issubstantially the same as the average contrast enhancement from T6 toT7. As another example, the second threshold 410 may be higher than thefirst threshold 412. FIG. 4B shows an example of the second section 422of the subject 112. The second section covers the abdomen. To completethe scan of the second section, a sequence of axial scans may beperformed in the direction along the length of the subject, as shownwith arrow 423. In FIG. 4B, the first section and the second section areconnected to each other at location 424. That is, the acquisition offirst dataset ends at 424 and the acquisition of the second datasetstarts at 424. In this example, the subject is not moved after acquiringthe first dataset and before acquiring the second dataset. In anotherembodiment, the first section and the second section may not beconnected with each other, or the first section and the second sectionare overlapped with each other. The subject is then moved uponcompletion of the acquisition of the first dataset at T3. For example,the first section is the head and the second section is the abdomen, andsubject is moved after acquiring the first dataset and before acquiringthe second dataset. At T8, the contrast enhancement decreases to zero.

In another embodiment, contrast enhancement curve 401 may include theenhancement of contrast agent in different sections of the subject. Forexample, the contrast enhancement from T1 to T5 is the contrastenhancement in the first section of the subject, and the contrastenhancement from T5 to T8 is the contrast enhancement in the secondsection of the subject. The physiological circulation of the contrastagent may be different in different sections of the human body. Forexample, the physiological circulation of contrast agent in head may belonger than the physiological circulation in abdomen. By using contrastenhancement of the imaged section, optimal image quality may beachieved.

Turning to FIG. 5, another example timeline of the contrast agentenhancement 510, the status of motor for driving the filter 520, and thestatus of the X-ray source 530 while implementing method 300 of FIG. 3are shown. Different from FIG. 4A, herein, a plurality of datasets ofthe first section of the subject are acquired with the first filter atmultiple time points while the contrast enhancement increases, and aplurality of datasets of the second section of the subject are acquiredat multiple time points with the second filter while the contrastenhancement decreases. As such, the phases of the contrast circulationin the subject may be obtained. In graph 510, the y-axis is theenhancement of contrast agent in the imaging subject. The contrast agentenhancement increases as indicated by the arrow of the y-axis. Curve 507shows the contrast enhancement over time. In one example, curve 507 maybe predetermined based on empirical knowledge (such as physiologicalcirculation) of the contrast agent, the dose, and the mass of thesubject. In another example, curve 507 may be estimated or measuredduring the contrast enhanced imaging. For example, the contrastenhancement may be periodically estimated or measured. Curve 507 may bethen generated by interpolating the estimated/measured contrastenhancement. In graph 520, the motor status may be on or off. When themotor is on, filters are switched. For example, the motor may beactivated to rotate a shaft coupled to the filters. By rotating theshaft, the filters maybe translated into and out of the X-ray beam path.In graph 530, the X-ray source status may be on or off. When the X-raysource is on, dataset of the imaging subject is acquired. In FIG. 5, thex-axes are time. The time increases as indicated by the arrows of thex-axes.

At T1, contrast agent is injected into the subject. Responsive to thecontrast agent administration, the contrast enhancement increases withtime from zero. The contrast enhancement increases from T1 to T6, anddecreases from T6 to zero at T10. From T1 to T6, multiple datasets ofthe first section of the subject are acquired using the first filter.From T6 to T10, multiple datasets of the second section of the subjectare acquired using the second filter. Upon completion of imaging thefirst section, the first filter is moved out of the X-ray path and isreplaced by the second filter by actuating one or more motors in thefilter driving system. The peak of the contrast enhancement curve 401may be anywhere between T5 and T7.

Each of the datasets may be acquired responsive to the contrastenhancement reaching a predetermined nonzero threshold. For example,acquisition of the first dataset starts at T2, responsive to thecontrast enhancement higher than the first threshold 501; acquisition ofthe second dataset starts at T3, responsive to the contrast enhancementhigher than the second threshold 502; and acquisition of the thirddataset starts at T4, responsive to the contrast enhancement higher thanthe third threshold 503. Acquisition of the fourth dataset starts at T7,responsive to the contrast enhancement lower than the fourth threshold504; acquisition of the fifth dataset starts at T8, responsive to thecontrast enhancement lower than the fifth threshold 505; and acquisitionof the third dataset starts at T9, responsive to the contrastenhancement lower than the third threshold 506. The thresholds may bechosen such that the average contrast enhancement while imaging thefirst and the second sections are substantially the same. For example,the average contrast enhancement while acquiring the first dataset issubstantially the same as the average contrast enhancement whileacquiring the sixth dataset; the average contrast enhancement whileacquiring the second dataset is the substantially same as the averagecontrast enhancement while acquiring the fifth dataset; and the averagecontrast enhancement while acquiring the third dataset is substantiallythe same as the average contrast enhancement while acquiring the fourthdataset. As such, at specific contrast enhancement, contrast enhancedimages of the first and the second sections of the subject may becomparable and displayed with the same dynamic range.

Similar to FIG. 4A, in one embodiment, the contrast enhancement curve507 may include contrast enhancement of different sections of thesubject. For example, curve 507 from T1 and T6 is the contrastenhancement in the first section of the subject. Curve 507 form T6 toT10 is the contrast enhancement in the second section of the subject.

FIG. 6 shows an example method 600 for imaging multiple differentanatomies of the imaging subject with fast filter switching. Method 600may be carried out according to instructions stored in thenon-transitory memory in a computing device (such as computer 216 ofFIG. 2) of the imaging system.

At 602, method 600 includes setting up scan parameters. For example, auser may input or select the scan parameters according to a scanningprotocol or a menu. The scan parameters may include the type andsequence of the filters that are going to be used during the scan. Thetype of the filters may be chosen based on the anatomy of imagingsubject that is to be imaged. Method 600 may also include setting scantiming. As one example, the scan timing may include a start time and aduration for imaging each section. Method 600 may also include loadinganatomy information of the imaging subject to the memory of thecomputation device. The anatomy information may be acquired from apre-scan. As another example, the anatomy information may be acquiredfrom a scout or a localized scan. This step may also include moving afilter to a position in the X-ray beam path between the X-ray source andthe subject, and moving the imaging subject via the motorized table(such as motorized table 228 of FIGS. 1-2) so that the proper section ofthe subject is within the gantry for imaging. The type of the filter isdetermined based on the anatomy of the currently imaged section of thesubject.

At 604, method 600 starts acquiring the dataset of the imaging subjectusing the first filter. Simultaneously, method 600 monitors the anatomyof the imaging subject. For example, the X-ray source (such as 104 ofFIGS. 1-2) may be activated, and start X-ray radiation exposure (such as106 of FIGS. 1-2) of the imaging subject through the first filter. Thedataset is acquired from the detector (such as 108 of FIG. 2) uponreceiving the transmitted radiation signal from the imaging subject. Asone example, the anatomy of the imaging subject may be monitored byanalyzing the acquired dataset. As another example, the anatomy of theimaging subject may be estimated by the currently imaged location. Thecurrently imaged location may be calculated based on the startinglocation of the scan and the travel distance of the motorized table. Inone embodiment, the anatomies of the subject may be grouped in differenttypes. For example, the anatomy of a human body may be grouped based onsize, into types of such as the head, the chest, and the abdomen. In oneembodiment, the acquisition of the dataset may be started responsive toa contrast agent enhancement higher than a threshold.

At 606, method 600 determines whether the scan is ended. Method 600 maydetermines the end of the scan based on the protocol setup at 602. Ifthe scan ends, method 600 proceeds to 608 to display and store theacquired dataset. If additional scan is needed, method 600 proceeds to610.

At 608, the acquired dataset is displayed and stored. In one embodiment,dataset acquired from different sections of the subject may bere-constructed to form an image. The image may be two-dimensional orthree-dimensional. The acquired dataset, as well as the processed imagesmay be saved in the storage of the imaging system.

At 610, method 600 determines whether the anatomy of the imaging subjectthat is being imaged has changed or is about to change. In oneembodiment, the anatomy may be determined to have changed when the sizeto type of the anatomy changes. Responsive to the change in anatomy,method 600 proceeds to 614 to switch the filter. Otherwise, method 600moves to 640 to continue acquiring the dataset with the current filterand monitoring the anatomy.

At 614, responsive the change in anatomy, the current filter is movedout of the X-ray beam path and a different filter is moved into theX-ray beam path. The filters may be moved by operating one or moremotors, such as motors shown in FIGS. 9A-9B. By moving the filters witha motor, filters may be automatically switched quickly within one scan.In one example, switching one filter with another filter may becompleted within two seconds. Step 614 may also include moving thesubject via the motorized table (such as motorized table of 228 in FIGS.1-2) to a predetermined location. The filter switching and subjectrelocation may be performed simultaneously. After filter switching,method 600 continues acquiring the dataset with the new filter andmonitoring the anatomy. In one embodiment, the data acquisition may becontinued through the filter switching process. In this way, time delaysbetween imaging different anatomies of the subject is reduced oravoided.

While method 600 is described above as including a filter switch that isperformed in response to a detected or predicted change in imagedanatomy, other triggers for switching the filters are possible. Forexample, the scanning protocol selected by the operator of the imagingsystem may include a series of images (reconstructed from acquiredprojection data) to be acquired along the imaging subject. A prescribedfirst set of images may be acquired while a first filter is in the X-raypath and while the imaging system table is at a first position. Once thefirst set of images has been acquired, the scanning protocol may commandor instruct the table to be moved to a second position in order to movethe imaging subject relative to the X-ray source and detector. Thescanning protocol may also command or instruct the filter driving systemto move the first filter out of the X-ray path and move a second filterinto the X-ray path. The filters may be moved/switched while the tableis moving. A prescribed second set of images may then be acquired whilethe second filter is in the X-ray path and the table is in the secondposition. In such a configuration, the switching of the filters may betriggered by a predetermined number of images (e.g., projection datasets) being acquired, by a predetermined amount of time having elapsedsince commencement of the scanning procedure, and/or by a user inputinstructing the filters to be switched.

FIG. 7 shows an example timeline of the status of the X-ray source 710the type of the anatomy 720, the speed of the motorized table (such asmotorized table 228 of FIGS. 1-2), and the status of the motor fordriving the filters 740 while implementing method 600 of FIG. 6. In oneexample, the imaging system performs helical scan of different types ofanatomy. In graph 710, the X-ray source status may be on or off. Whenthe X-ray source is on, a dataset of the imaging subject is acquired. Ingraph 720, different types of the anatomy is shown. For example, thefirst type of the anatomy is the head, the second type of the anatomy ischest, and the third type of the anatomy is the abdomen. In graph 730,the speed of the motorized table for moving the subject is shown. Thespeed increases with the y-axis. In graph 740, the motor status may beon or off. When the motor is on, filters are switched. For example, themotor may be activated to rotate a shaft coupled to the filters. Byrotating the shaft, the filter maybe translated into and out of theX-ray beam path.

At T1, the X-ray source is turned on for imaging the first type of theanatomy. A filter designed for imaging the first type of anatomy ispositioned between the X-ray source and the imaging subject. Themotorized table is moved at a nonzero speed to translate the subjectthrough the gantry for the scan. The motor for driving the filter isoff. In one embodiment, the X-ray source may be started responsive to anenhancement of the contrast agent higher than a nonzero threshold.

At T2, the anatomy being imaged or to be imaged changes from the firsttype to the second type. Responsive to the change, the motor for drivingthe filter is actuated to switch the current filter to a differentfilter designed for imaging the second type of anatomy. The duration forswitching the filter lasts ΔT, which is less than two seconds. Themotorized table may be operated at a different speed from prior to T2and move the imaging subject to a section with different anatomy. As oneexample, the motorized table may be moved at a higher speed from T2 toT3 comparing to prior to T2. As another example, the motorized table maybe stationary and the speed is zero from T2 to T3. As yet anotherexample, the motorized table may move at the same speed as during T1-T2.While switching the filter, the X-ray source is turned off and no X-rayradiation exposure is emitted to the imaging subject. As such, theoverall patient X-ray radiation dose may be reduced. In one embodiment,the duration for moving the imaging subject (T2-T3) may be greater thanthe duration for switching the filter (ΔT), and the X-ray source isturned off while moving the imaging subject.

From T3 to T4, the second type anatomy is imaged and the motorized tableis moved at a low speed. As one example, the speed of the motorizedtable from T3 to T4 is the same as the speed of the motorized table fromT1 to T2.

At T4, the anatomy being imaged or to be imaged changes from the secondtype to the third type. Responsive to the change, the motor for drivingthe filter is actuated to switch the current filter to a differentfilter designed for imaging the third type of anatomy. During T4 to T5,the motorized table may move at a different speed from during T3-T4. TheX-ray source is turned off while switching the filter.

From T5 to T6, the third type anatomy is imaged and the motorized tableis moved at a low speed. As one example, the speed of the motorizedtable from T5 to T6 is the same as the speed of the motorized table fromT3 to T4.

At T6, the scan is finished. The speed of the motorized table goes tozero and the X-ray source is turned off.

FIGS. 8A-8D show an example configuration of a filter assembly withthree filters 805, 806, and 807 within filter housing 810. In thisexample, the first and second filters are positioned together in ahousing 804. The housing 804 is coupled to a ballscrew 811, and can betranslated along the first shaft 808 by rotating the first shaft with afirst motor 802. The third filter 807 is coupled to a ballscrew 812 andcan be translated along the second shaft 809 by rotating the secondshaft with the second motor. A localized clearance feature (not shown)is present in the housing 804 to prevent interference of the secondshaft 809 from interfering with the housing 804 as the housing 804translates along the first shaft 808. The direction of the X-ray beam(such as X-ray radiation 106 of FIGS. 1-2) is indicated by 801. One ofthe three filters may be translated into the beam path of the X-ray beamby rotating one or both shafts 808 and 809 via motors 802 and 803. Thefirst and the second shafts may be aligned in one line along the shafts,and are spaced apart from each other by a gap 813. The X-ray beam maytransmit through the gap. The motor (such as motor 803), the shaft (suchas shaft 809) coupled to the motor, and the filter (such as filter 807)coupled to the shaft form a filter driving system 890. The filterassembly may include one or more filter driving systems. Exampleconfiguration of the filter driving system is shown in FIGS. 9A-9B.

FIG. 8A shows a first position of the filter assembly. The X-ray beamtransmits through the filter housing without passing through any filter.The first and the second filters are at a location close to the firstmotor 802, and the third filter is at a location close to the secondmotor 803.

FIG. 8B shows a second position of the filter assembly. The X-ray beamtransmits though the first filter 805 in the filter housing 810. Thefilter assembly may transit from the first position to the secondposition by actuating the first motor 802 and translating the firstfilter 805 into the X-ray beam path.

FIG. 8C shows a third position of the filter assembly. The X-ray beamtransmits though the second filter 806 in the filter housing 810. Thefilter assembly may transit from the first position or the secondposition to the third position by actuating the first motor 802 andtranslating the second filter 806 into the X-ray beam path.

FIG. 8C shows a fourth position of the filter assembly. The X-ray beamtransmits through the third filter 807 in the filter housing 810. Thefilter assembly may transit from either the second or the thirdpositions to the fourth position by actuating the first motor 802 totranslate the housing 804 closer to the first motor 802, andsubsequently or simultaneously actuating the second motor 803 totranslate the third filter into the X-ray beam path.

Based on the instructions stored in the non-transient memory, thecomputing device (such as computing device 216 of FIG. 2) may move thefilter assembly from any one of the above positions to another positionby actuating one or more of the two motors. In one embodiment, twofilters are positioned in the filter housing. As one example, the twofilters may be coupled to one shaft and driven by one motor. As anotherexample, one of the two filters is coupled to one shaft and driven byone motor, and the other of the two filters is coupled to a second shaftand driven by a second motor. In another embodiment, more than threefilters may arranged within the filter housing. For example, the numbersof filters coupled to each shaft are the same, if the total number offilters in the housing is even. The numbers of filters coupled to eachshaft is different, if the total number of filters in the housing isodd. As such, duration of filter switching may be reduced due to lowaverage filter distance from the X-ray beam path.

In yet another embodiment, the arrangement of the filters in the filterhousing may be based on the type of the filters. Herein, the filter typemay be determined by the section of the subject that the filter isdesigned to image. For example, the first filter used for imaging thefirst section of the subject and the second filter used or imaging thesecond section of the subject may be positioned next to each other, ifthe first section and the second section are connected. The first filterand the second filter may be positioned apart from each other (such asseparated by another filter), if the first section and the secondsection are not connected. As an example, the filter for imaging theabdomen maybe positioned next to the filter for imaging the chest, butapart from the filter for imaging the head. In this way, when the chestis imaged after imaging the abdomen, the filters may be quickly switchedfrom one to another. When the head is imaged after imaging the abdomen,the duration for filter switching may be longer, as the imaging subjectneeds to be physically moved from imaging the abdomen to imaging thehead.

FIGS. 9A and 9B show examples of the filter driving system. Each filterassembly (such as filter assembly shown in FIGS. 8A-8D) may have one ormore of the filter driving systems.

FIG. 9A shows an example configuration of the filter driving system.Filter 906 is mechanically coupled to a ballscrew nut 904. The ballscrewshaft 902 is mechanically coupled to motor 903 via shaft 908. As motor903 rotates, the filter 906 may translate in directions indicated byarrow 907 along the ballscrew shaft 902. As such the rotational motionof the shaft is translated to linear motion of the filter along theshaft. The motor is fixed to support 901. A second filter 905 may becoupled to filter 906. The filter 905 and filter 906 are not movablerelative to each other. As such, filters 905 and 906 are translatedtogether along the ballscrew shaft 902.

FIG. 9B shows another example configuration of the filter drivingsystem. Filter 926 is mechanically coupled to ballscrew nut 924. Theball screw nut is coupled to motor 923 via shaft 910, flex coupling 929,and shaft 928. The flex coupling is positioned between shaft 910 andshaft 928. Shaft 910 is directly coupled to the ballscrew shaft 922, andshaft 928 is directly coupled to motor 923. The flex coupling mayincrease the tolerance of misalignment between the motor 923 and theballscrew shaft 922. The ballscrew shaft 922 is supported by supportbearings 912 and 913 at each distal end of the shaft. By rotating themotor 923, the filter 926 may translate in directions as shown by arrow927. A second filter 925 may be coupled to filter 926. The filter 925and filter 906 are not movable relative to each other. As such, filters905 and 906 are translated together along the ballscrew shaft 922.

In other embodiments, the filter may be translated with any one of arack and pinion, a belt, or a cable-driven system.

The filter driving system in the filter assembly switches one filter toanother within two seconds. For example, the filter can be translated3-5 inches in less than two seconds by the filter driving system.

In this way, mixed-size anatomy may be imaged with high image qualityduring time-sensitive scans such as contrast enhanced imaging. Thetechnical effect of switching filters after the contrast agent injectionis that different anatomies of the subject may be imaged with onecontrast agent injection. The technical effect of actuating the motor toswitch the filters is that the duration for switching the filters may bereduced. The technical effect of acquiring dataset responsive tocontrast enhancement is that the average contrast enhancement indifferent imaged anatomies may be the same, and the dataset may bedisplayed with the same dynamic range for diagnostic analysis.

In one embodiment, a method comprises monitoring the contrastenhancement; responsive to a first contrast enhancement being higherthan a first threshold, acquiring a first dataset of the imaging subjectby transmitting a X-ray beam to the imaging subject via a first filter;switching to a different, second filter after acquiring the firstdataset; and acquiring a second dataset of the imaging subject bytransmitting the X-ray beam to the imaging subject via the secondfilter. In a first example of the method, wherein acquiring the seconddataset comprises acquiring the second dataset without additionalcontrast agent being injected to the imaging subject between theacquisition of the first dataset and the acquisition of the seconddataset. A second example of the method optionally includes the firstexample and further includes wherein both the first filter and thesecond filter are non-deformable. A third example of the methodoptionally includes one or more of the first and second examples, andfurther includes wherein an average contrast enhancement of the injectedcontrast agent in the imaging subject during the acquisition of thefirst dataset is substantially the same as an average contrastenhancement of the injected contrast agent in the imaging subject duringthe acquisition of the second dataset. A fourth example of the methodoptionally includes one or more of the first through third examples, andfurther includes, measuring a second contrast enhancement of theinjected contrast agent within the imaging subject, and acquiring thesecond dataset of the imaging subject with the second filter responsiveto the second contrast enhancement being less than a second threshold. Afifth example of the method optionally includes one or more of the firstthrough fourth examples, and further includes, wherein both the firstthreshold and the second threshold are nonzero, and the second thresholdis higher than the first threshold. A sixth example of the methodoptionally includes one or more of the first through fifth examples, andfurther includes, wherein the first contrast enhancement of the injectedcontrast agent is a contrast enhancement of the injected contrast agentwithin a first section of the imaging subject, and the second contrastenhancement of the injected contrast agent is a contrast enhancement ofthe injected contrast agent within a second section of the imagingsubject. A seventh example of the method optionally includes one or moreof the first through sixth examples, and further includes, wherein afirst section of the imaging subject is imaged while acquiring the firstdataset, and a different, second section of the imaging subject isimaged while acquiring the second dataset. An eighth example of themethod optionally includes one or more of the first through seventhexamples, and further includes, wherein the first section of the imagingsubject and the second section of the imaging subject have differentanatomies. A ninth example of the method optionally includes one or moreof the first through eighth examples, and further includes, whereinswitching to the second filter includes operating one or more motorscoupled to the first filter and the second filter to translate the firstfilter out of the X-ray beam and translate the second filter into theX-ray beam. A tenth example of the method optionally includes one ormore of the first through ninth examples, and further includes,displaying the first dataset and the second dataset simultaneously witha same dynamic range.

In another embodiment, a method comprises measuring a contrastenhancement of an injected contrast agent within an imaging subject;responsive to the contrast enhancement being higher than a first nonzerothreshold, acquiring a first number of a first dataset, wherein thefirst dataset is acquired by transmitting a X-ray beam to the firstsection of the imaging subject via a first filter; switching to adifferent, second filter after acquiring the first number of the firstdatasets; acquiring second number of a second dataset by transmittingthe X-ray beam to a different, second section of the imaging subject viathe second filter, wherein the contrast enhancement of the injectedcontrast agent with in the imaging subject is higher than the firstthreshold while acquiring the second number of the second datasets. In afirst example of the method, the first number is the same as the secondnumber. A second example of the method optionally includes the firstexample and further includes determining a time point to start acquiringeach of the first and second datasets based on the contrast enhancementof the injected contrast agent within the imaging subject. A thirdexample of the method optionally includes one or more of the first andsecond examples, and further includes wherein the first filter and thesecond filter are bowtie filters.

In yet another embodiment, an imaging system comprises a gantry forreceiving an imaging subject; a X-ray source positioned in the gantryfor emitting X-ray radiation exposure; a detector positioned on theopposite of the gantry relative to the X-ray source; a filter housingmounted to the gantry; a first filter and a second filter positioned inthe filter housing; a filter driving system for switching filters bymoving filters into or out of the X-ray radiation exposure; a motorizedtable for moving an imaging subject; and a computation device withinstructions stored in a non-transient memory, the computation devicemay execute the instructions to: emit X-ray radiation exposure via theX-ray source; move the imaging subject via the motorized table at anonzero speed; while moving the imaging subject, acquire a dataset ofthe imaging subject by detecting the emitted X-ray radiation exposuretransmitted through the imaging subject via the detector, wherein afirst filter is positioned within the emitted X-ray radiation exposure,between the X-ray source and the imaging subject; and while acquiringthe dataset, estimate the anatomy of the imaging subject, responsive toa change in the anatomy, operate the filter driving system to switch thefirst filter with the second filter, wherein during filter switching,the X-ray source does not emit X-ray radiation exposure. In a firstexample of the imaging system, the computation device may execute theinstructions to further monitor a contrast enhancement of an injectedcontrast agent, and start acquiring the dataset responsive to thecontrast enhancement higher than a nonzero threshold. A second exampleof the imaging system optionally includes the first example and furtherincludes, wherein the filter driving system includes a motor coupled tothe first filter and the second filter via a shaft, and switching thefirst filter with the second filter includes actuating the motor totranslate the first filter out of the X-ray beam, and translate thesecond filter into the X-ray beam. A third example of the imaging systemoptionally includes one or more of the first and second examples, andfurther includes, wherein the first filter is different from the secondfilter, and the acquired dataset are from a plurality of differentanatomies of the imaging subject. A fourth example of the imaging systemoptionally includes one or more of the first and third examples, andfurther includes wherein a duration for switching the first filter tothe second filter is less than two seconds.

As used herein, an element or step recited in the singular and proceededwith the word “a” or “an” should be understood as not excluding pluralof said elements or steps, unless such exclusion is explicitly stated.Furthermore, references to “one embodiment” of the present invention arenot intended to be interpreted as excluding the existence of additionalembodiments that also incorporate the recited features. Moreover, unlessexplicitly stated to the contrary, embodiments “comprising,”“including,” or “having” an element or a plurality of elements having aparticular property may include additional such elements not having thatproperty. The terms “including” and “in which” are used as theplain-language equivalents of the respective terms “comprising” and“wherein”. Moreover, the terms “first,” “second,” and “third,” etc. areused merely as labels, and are not intended to impose numericalrequirements or a particular positional order on their objects.

This written description uses examples to disclose the invention,including the best mode, and also to enable a person of ordinary skillin the relevant art to practice the invention, including making andusing any devices or systems and performing any incorporated methods.The patentable scope of the invention is defined by the claims, and mayinclude other examples that occur to those of ordinary skill in the art.Such other examples are intended to be within the scope of the claims ifthey have structural elements that do not differ from the literallanguage of the claims, or if they include equivalent structuralelements with insubstantial differences from the literal languages ofthe claims.

What is claimed is:
 1. An imaging system, comprising: a gantry forreceiving an imaging subject; an X-ray source positioned in the gantryfor emitting an X-ray beam; an X-ray detector positioned in the gantryopposite to the X-ray source; a filter assembly mounted in the gantry; afirst filter and a second filter positioned in the filter assembly; afilter driving system for switching filters by moving filters into orout of the X-ray beam; a motorized table for moving an imaging subject;and a computation device with instructions stored in a non-transientmemory to: emit the X-ray beam via the X-ray source; move the imagingsubject via the motorized table at a nonzero speed; while moving theimaging subject, acquire a dataset of the imaging subject by detectingattenuated X-rays transmitted through the imaging subject via the X-raydetector, wherein a first filter is positioned within the X-ray beam,between the X-ray source and the imaging subject; and while acquiringthe dataset, responsive to a change in an anatomy of the imaging subjectto be imaged, operate the filter driving system to switch from the firstfilter to a second filter, wherein during filter switching, the X-raysource does not emit X-rays.
 2. The imaging system of claim 1, whereinthe computation device includes further instructions to determine acontrast enhancement of an injected contrast agent, and start acquiringthe dataset responsive to the contrast enhancement being higher than anonzero threshold.
 3. The imaging system of claim 1, wherein the filterdriving system includes a motor coupled to the first filter and thesecond filter via a shaft, and switching from the first filter to thesecond filter includes actuating the motor to translate the first filterout of the X-ray beam, and translate the second filter into the X-raybeam.
 4. The imaging system of claim 1, wherein the first filter isdifferent from the second filter, and the acquired dataset is from aplurality of different anatomies of the imaging subject.
 5. The imagingsystem of claim 1, wherein switching from the first filter to the secondfilter takes less than two seconds.